Throttle assembly for internal combustion engine, and throttle sensor

ABSTRACT

In a throttle body there are provided a throttle valve for controlling the flow of intake air in an internal combustion engine, an electrically-driven actuator for actuating the throttle valve, and a reduction gear mechanism for the actuator, and a receptacle portion for receiving the reduction gear mechanism therein is formed in a side wall of the throttle body. A cover which covers the receptacle portion is attached to a side wall of the throttle body. The throttle assembly of the invention is provided with a potentiometer type sensor for detecting the degree of opening of the throttle valve, the sensor comprising a slider and a resistor, the slider being adapted to slide on the resistor and mounted to a peripheral surface of a driven gear so that a tip end thereof faces in a radial direction of a throttle valve shaft, the driven gear being disposed on the throttle valve shaft side of the reduction gear mechanism. On the other hand, the resistor is constituted by a curved resistor which confronts the slider in the said radial direction. A wall portion which holds the curved resistor is formed by molding integrally with the aforesaid cover.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a throttle assembly for controlling theflow (amount of the flow) of intake air in an internal combustionengine, as well as a throttle sensor for detecting the degree of openingof a throttle valve used in the throttle device.

2. Background Art

Heretofore, an electronically controlled throttle assembly haspractically been used wherein the operation of a throttle valve in anengine is controlled by an electrically-driven actuator (e.g., a DCmotor or a stepping motor).

The electronically controlled throttle assembly controls the throttlevalve angle (throttle valve opening) to an optimum value according tothe state of an engine and in accordance with a signal indicative of thedegree of opening of an accelerator pedal or a traction control signal.To this end, a sensor for detecting the angle of the throttle valve,what is called a throttle sensor (also called an opening meter or athrottle position sensor) is attached to a throttle body.

As the throttle sensor there generally is adopted a potentiometer typesensor, wherein a brush (slider) adapted to rotate together with athrottle valve shaft slides on a resistor, thereby outputting apotential difference signal (sensor detection signal) corresponding tothe degree of opening of a throttle valve.

As throttle sensors of this type so far used there are known, forexample, such throttle sensors as are disclosed in Japanese Patent LaidOpen Nos. 7-343878 and 9-32588, wherein a resistor and a wiring patternof a potentiometer are formed on a substrate. The substrate is attachedto a cover of a receptacle portion containing a reduction gearmechanism. A brush is attached to a flat surface of a driven gear (or arotor) mounted on a throttle valve shaft. In this type of a throttlesensor, the brush slides on a resistor and a conductor both formed onthe substrate (a flat surface). Since the driven gear is used also as amoving element to which the brush of the potentiometer is attached, thenumber of components used can be so much reduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a throttle devicecapable of contributing to reducing the number of components of athrottle sensor, capable of reducing the manufacturing cost andsimplifying the assembling work, and further capable of ensuring highaccuracy and reliability of the sensor.

DISCLOSURE OF INVENTION

For achieving the above-mentioned object the present invention basicallyproposes the following throttle assemblies:

-   (1) A throttle assembly comprising a throttle body having a throttle    valve, an electrically-driven actuator for actuating the throttle    valve, and a sensor for detecting the degree of opening of the    throttle valve,

wherein the sensor is constituted by a potentiometer whose output variesaccording to the rotation of a throttle valve shaft and which comprisesa slider (also called a brush) and a resistor, the slider being adaptedto slide on the resistor and disposed on one end side of a throttlevalve shaft so that a tip end thereof faces in a radial direction of thethrottle valve shaft, the resistor being formed as an arcuately curvedsurface (what is called a curved resistor), and a wall portion whichholds the curved resistor is formed by molding integrally with a coverwhich covers the one end side of the throttle valve shaft in thethrottle body.

According to a preferred example of the above throttle device (1), theperipheral resistor holding portion (wall portion) is formed by moldingintegrally with the cover, as described above, and the slider isattached to a peripheral portion of a gear (a driven gear as afinal-stage gear in a reduction gear mechanism) mounted on the throttlevalve shaft.

-   (2) A throttle assembly comprising a throttle body and, as    components mounted to the throttle body, a throttle valve for    controlling the flow of intake air in an internal combustion engine,    an electrically-driven actuator for actuating the throttle valve, a    reduction gear mechanism for the actuator, and a sensor for    detecting the degree of opening of the throttle valve,

wherein one end of a throttle valve shaft is projected outwards from aside wall of the throttle body, the reduction gear mechanism and thesensor are disposed on a side face of the throttle body on theprojecting side of the throttle valve shaft,

a bearing which supports one end of the throttle valve shaft on theprojecting side of the throttle valve shaft, out of bearings whichsupport the throttle valve shaft, is a ball bearing, a bearing locatedon the opposite side of the throttle valve shaft is a cap-shaped plainbearing, and one bearing boss of the throttle valve shaft is coveredwith the plain bearing.

-   (3) A throttle sensor for detecting the degree of opening of a    throttle valve which controls the flow of intake air in an internal    combustion engine,

wherein the throttle sensor is constituted by a potentiometer whoseoutput varies according to the rotation of the throttle valve, thepotentiometer comprising a slider adapted to rotate integrally with athrottle valve shaft and a resistor on which the slider slides, theresistor being connected at one end thereof to a positive-side terminalof a power supply and at an opposite end thereof to a ground-sideterminal, the position at which the resistor contacts the slider is anoutput point for taking out an output voltage, and an auxiliary resistor(or resistors) is connected either between one end of the resistor andthe positive-side terminal of the power supply or between the oppositeend of the resistor and the ground-side terminal, or both. In otherwords, an auxiliary resistor is provided at one end or at each of bothends of the resistor which is a component of the potentiometers

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view of a throttle assembly accordingto an embodiment of the present invention and FIG. 2 is a plan viewshowing a throttle body used in the embodiment, with a cover 16 removedfrom the throttle body to see the uncovered interior. A gear indicatedat 12 in

FIG. 2 is mounted to a throttle valve shaft on the throttle body side,but in the same figure, for understanding in what positional relationthe gear 12 is inside the gear cover 16, the gear 12 alone is removedfrom the throttle valve shaft 3 and is illustrated together with thegear cover.

FIG. 3 is a partial perspective view showing the state of FIG. 2rspectively,

FIGS. 4, 5 and 6 are exploded perspective views showing the throttleassembly of this embodiment as seen in different angles,

FIG. 7 is a perspective view showing, in a disassembled state,components of a throttle sensor which is attached to the cover,

FIG. 8 is a perspective view showing a driven gear with brush (slider)which is one of reduction gears used in the embodiment,

FIG. 9 is a side view of the cover,

FIG. 10 is a sectional view showing the driven gear as mounted to athrottle valve shaft,

FIGS. 11 and 12 are sectional views showing other examples of drivengears,

FIG. 13 is a developed view of a film with resistor used in the throttlesensor,

FIG. 14 is a circuit diagram of resistors and wiring patterns shown inFIG. 13,

FIG. 15 is an equivalent circuit diagram thereof, and

FIG. 16 is an operation characteristic diagram of the throttle sensorused in the embodiment.

DESCRIPTION OF THE PEEFERRED EMBODIMENTS

An embodiment of the present invention will be described hereinunderwith reference to the accompanying drawings.

As shown in FIG. 1, an electronically controlled throttle assembly(throttle valve assembly) is composed principally of a throttle body 1,which may be referred to simply as the body hereinafter, a throttlevalve 4, a motor (a throttle valve driving unit or anelectrically-driven actuator) 22 for actuating the throttle valve 4, areduction gear mechanism 100, a sensor (throttle sensor) 101 fordetecting the angle (degree) of opening, which may be referred to simplyas opening hereinafter, of the throttle valve 4, and a cover 16 forprotecting a throttle valve shaft 3, motor 22 and reduction gearmechanism 100.

The body 1 is formed by molding a receptacle portion (intake bore) 2 forthe throttle valve 4 and a receptacle portion (motor housing) 1 c forthe motor 22 integrally with each other. The throttle valve 4 is mountedto the shaft 3 with screws 5, and the shaft 3 is supported by bearings 6and 26 which are installed in the body 1.

Various bearings are mentioned as examples of the bearing 6, among whicha ball bearing has heretofore been used as a bearing usually adopted. Inthis embodiment, a ball bearing and a cap-shaped plain bearing are usedas the bearings 6 and 26, respectively. The reason therefor and theirdetails will be described later. The ball bearing 6 is secured to abearing boss 1 a through a seal ring 8. An inner ring 6 a of the ballbearing 6 is press-fitted on an outer periphery of the throttle valveshaft 3, while an outer ring 6 b thereof is fitted in an inner peripheryof the bearing boss 1 a by transition fit (sliding fit).

Only one end of the throttle valve shaft 3 projects to the exterior of aside wall of the body 1, and a spring 10, a lever 9, a spring 11, and afinal-stage gear (driven gear) 12 in the reduction gear mechanism 100,which will be described later, are fitted on the projecting one end ofthe throttle valve shaft. The plain bearing 26 is mounted bypress-fitting for examples.

Throttle valve-related components (hereinafter referred to as thethrottle valve mechanism) such as the throttle valve shaft 3, reductiongear mechanism 100 and motor 22 are accommodated within a receptacleportion (case) Id formed in a side wall of the body 1, the receptacleportion id being covered with a synthetic resin cover 16.

More specifically, the throttle valve mechanism is disposed so as to beprotected by a single cover 16, an opening (a motor mounting opening) 1c′ of the motor housing 1 c is positioned so as to face the interior ofthe receptacle portion 1 d, through which opening the motor 22 isreceived into the housing, and an end bracket 22 a of the motor is fixedwith screws 37 around the opening 1 c′ (see FIGS. 4 to 6).

Motor terminals 23 formed on the end bracket 22 a are positioned near aside wall of the receptacle portion 1 d so as to face toward the cover16 and are connected to relay terminals 24 a through relay connectors33. The relay connectors 33 may be in any of various forms. In thisembodiment, sleeves are used as the relay connectors 33, slits 34 and 35(see FIG. 5) are formed respectively in both ends of each of the slitsin 90°-shifted directions, and each motor terminal 23 and relay terminal24 a are fitted in the slits 34 and 35. The terminals 23 and 24 a alsoface in 90°-shifted directions to match the extending directions of theslits 34 and 35.

The motor 22 is driven in accordance with an accelerator signal relatedto the depression quantity of an accelerator pedal and a tractioncontrol signal, and the power of the motor 22 is transmitted to thethrottle valve shaft 3 through the reduction gear mechanism 100 (a motorpinion 21, an intermediate gear 20, and the final-stage fear 12). Thepinion 21 is mounted on a motor shaft 27 and the intermediate gear 20 isfitted free on a shaft 19 which is fixed to the throttle body 1. Theintermediate gear 20 comprises a gear 20 a of a larger diameter meshingwith the pinion 21 and a gear 20 b of a smaller diameter meshing withthe gear 12.

The final-stage gear 12 is a sectorial gear and, as shown in FIGS. 2 to6 and FIG. 8, a holder 12 c for holding brushes (sliders) 13 of apotentiometer is integral with the gear 12. The holder 12 c is formed soas to be positioned on a peripheral surface of the gear 12 on the sideopposite to a toothed area of the same gear.

Before describing features of the gear 12 in detail, reference willfirst be made to the relation between the gear 12 and the lever 9. Asshown in FIG. 8, the gear 12 has a hole 12 h for passing one end 3 a′(having at least two flat surfaces) of the throttle valve shaft 3therethrough. The hole 12 h is formed in a shape engageable with the oneend 3 a′ of the throttle valve shaft, and through this engagement thegear 12 rotates integrally with the throttle valve shaft 3.

The lever 9 is fitted free on the outer periphery (circumferentialsurface) of the throttle valve shaft 3 so that the lever 9 and the gear12 are pulled toward each other-through a spring 11. For example, a lugindicated at 12 f in FIGS. 2 to 4 comes into engagement with a lug 9 aof the lever 9 shown in FIG. 6. The lug 12 f is formed inside the gear12. Further, a lug 12 g formed on the gear 12 is for positioning in anassembling work relative to a lug 9 b formed on the lever 9 side.

A spring 10 is a return spring for the throttle valve. One end of thespring 10 is anchored to a spring retaining portion (not shown) providedon the body 1 side and the opposite end thereof is anchored to the lever9.

The spring 10, which imparts a return force to the throttle valve shaftthrough the gear 12, constitutes a known default opening settingmechanism in cooperation with the spring 11 and the lever 9.

The default opening setting mechanism is for holding an initial openingof the throttle valve larger than a fully closed position during OFF ofan engine key (in other words, while the electrically-driven actuator 22is de-energized). From a default opening position up to a fully opencontrol position, a throttle valve opening is determined in accordancewith the balance between the motor power and the spring (return spring)10. For controlling the throttle valve opening smaller than the defaultopening, the movement of the lever 9 is prevented by a default openingstopper (not shown) and only the gear 12 and the throttle valve shaft 3are turned in fully closing direction against the force of the spring11. Numeral 25 denotes a fully closing stopper which defines amechanical fully closed position of the throttle valve, which fullyclosed position is determined by abutment of a movable-side stopper 12 dagainst the stopper 25, the stopper 12 d being formed on one side of thesectorial gear 12. The stopper 12 d is fixed with a nut 25 a.

As to the material of the gear 12 used in this embodiment, as is seenfrom a sectional view of FIG. 10, a central portion is constituted by ametallic plate 12 a, and a teeth-forming portion 12 b, the brush holder12 c and the remaining portion are formed integrally by molding asynthetic resin (a reinforced plastic). In this case, the metallic plate12 a is insert-molded into the resin portion of the gear. Themovable-side stopper 12 d is integral with the metallic plate 12 a.

The stopper 12 d is formed of a metal for improving the accuracy of thestopper position. More particularly, the mechanical fully closedposition of the throttle valve serves as a reference point in controland the stopper 12 d strikes against the fixed-side fully closingstopper 25 once at every beginning or end of operation. Thus, a highaccuracy is required for the stopper 12 d, and for this reason thestopper 12 d is formed of a metal which is high in rigidity.

The gear 12 is further provided with a movable-side stopper 12 e fordefining a fully open position of the throttle valve (FIGS. 2 and 8).The stopper 12 e is formed by molding a synthetic resin integrally withthe gear 12 and the brush holder 12 c. It suffices for the movable-sidefully opening stopper 12 e to be formed of a synthetic resin because thestopper 12 e generally does not strike against any other componentduring operation. Numeral 12 i denotes a guide for engagement of thegear 12 with the lever 9.

The holder 12 c for holding the brushes 13 is formed on a peripheralsurface of the gear 12, and two brushes 13 are arranged on an outersurface of the holder 13 c side by side in the axial direction of thegear 12. A rotational radius from the throttle valve shaft 3 up to thetips of the brushes 13 is set larger than that of the driven gear 12.The reason why two brushes 13 are used is that it is intended to use adual system (two) of throttle sensors. The dual system is advantageousin that even in the event of failure of one throttle sensor, the othercan be used as a substitute and that even in the event of occurrence ofany trouble on one sensor side, the trouble can be detected byprocessing signals provided from both sensors.

For example, as shown in FIG. 8, the brushes 13 are fitted on lugs 12 jformed on the holder 12, which lugs 12 j are then crushed with heat tofix the brushes onto the holder. Alternatively, the brushes 13 may befixed using screws or an adhesive.

The gear 12 is fixed to one end 3′ of the throttle valve shaft 3 withuse of a nut 17 and a washer 18.

The gear 12 is not limited to the one described above. Such gears asillustrated in FIGS. 11 and 12 are also employable.

In the gear 12 illustrated in FIG. 11, the portion of the brush holder12 c is formed of a synthetic resin, while the teeth-forming area 12 band the remaining portion are formed using a sintered metal, and thebrush holder 12 c is outer-molded to the gear 12 with use of a resin.

In the gear 12 illustrated in FIG. 12, all the constituent portions ofthe gear 12, including the brush holder 12 c, are formed using asynthetic resin, which resin is insert-molded into one end 3 a of thethrottle valve shaft 3, thus dispensing with the nut 17 and the washer18.

The following description is now provided about the cover 16.

A great feature of the cover 16 used in this embodiment is that a stator(resistors and wiring patterns) which constitutes the throttle sensor(potentiometer) 101, as well as a wall portion 15 which holds the statorare provided directly in the cover 16.

Heretofore, for reducing the number of components of a throttleassembly, there has been made an attempt to secure a brush directly to adriven gear in a reduction gear mechanism, but if the member for holdingresistors and wiring patterns (conductors) in a potentiometer can beformed by molding integrally with the cover 16, there can be made afurther contribution to the reduction in the number of components.

However, in case of forming resistors and wiring patterns directly on aninner surface of the cover 16, since the cover 16 is formed of asynthetic resin, the resistors may be deteriorated in accuracy under theinfluence of thermal expansion, contraction and deformation of thecover. According to a conventional measure adopted for avoiding such aninconvenience, resistors and wiring patterns are formed on a substrateas a separate member from the cover and the substrate is then attachedto the inner surface of the cover.

This embodiment intends to make it possible to mold the holding member(wall portion) 15 for the potentiometer (especially resistors and wiringpatterns) integrally with the cover 16 while minimizing the influence ofsuch thermal expansion, contraction and deformation of the cover as justreferred to above, and to this end the following means is adopted in theembodiment.

As a basic structure, the wall portion 15 is formed by bending a thinplate in a curvilinearly projecting shape so as to minimize the areathereof occupied on the cover 16 and by raising, like erection, thethus-curved thin plate from the inner surface of the cover. According tosuch an arcuately curved shape of the wall portion 15, not only thethermal expansion and contraction of the wall portion can be kept to aminimum, but also the wall portion can be enhanced in its rigidity andis difficult to be thermally deformed. In this embodiment, moreover, areinforcing rib 15 d is formed on the back of the wall portion 15 toenhance the strength of the wall portion.

As to the brushes 13, they are mounted on the peripheral surface throughthe holder 12 c so that their tips face in the radial direction of thethrottle valve shaft 3. The brushes 13 may be mounted to a componentother than the gear 12. For example, a rotor used exclusively for thebrush holder may be attached to one end 3 a′ of the throttle valve shaft3.

Resistors R1 and R2 (see FIG. 13) on which the brushes 13 slide areformed on one side of a film 14 by printing together with auxiliaryresistors R3, R4, conductors 150, 151, 151′ which constitute wiringpatterns, conductors 141, 142 for taking out signals, and terminals161˜164. As shown in FIGS. 2, 3 and 4, these registers and conductorsare arcuately curved together with the film 14. Thus, the resistors R1and R2 are formed as curved resistors.

The reason why two resistors R1 and R2 are used in the potentiometer andso are the brushes 13 is because it is intended to form two throttlesensors. As to operational characteristics of the potentiometer used inthis embodiment, reference will be made thereto later.

In the other figures than FIG. 13, for example in FIGS. 2, 3, 4 to 6 and7, the curved resistors R1 and R2 are omitted their illustration for theconvenience of drawing. For convenience sake, the film 14 mayhereinafter be referred to as the curved resistor or film withresistors.

As noted earlier, the wall portion 15 which holds the curved resistor 14(i.e., film with resistors R1 and R2) is formed by molding integrallywith the cover 16 which covers one end side of the throttle valve shaftof the throttle body 1.

As shown in FIG. 2, the wall portion 15 is formed in conformity with thedirection of the bushes 13 and is positioned on the inner surface of thecover 16 and near the corner located on the side opposite to the teethportion of the gear 12. The wall portion 15 is in a curvilinearlyerected shape which draws an arc about the axis of the throttle valveshaft 3.

Now, with reference to FIGS. 13 to 15, a description will be given belowabout the circuit configuration of the potentiometer and related wiringlayout used in this embodiment.

As shown in FIG. 13, the conductor 141 for taking out an output signaland the resistor R1, as well as the conductor 142 for taking out anoutput signal and the resistor R2, are arranged in parallel on one sideof the synthetic resin film (sheet) 14, with auxiliary resistors R3 andR4 being further added.

The conductors 141 and 142 are formed using a material of a lowresistivity, e.g., silver paste, while the resistors R3 and R4 areformed using a material of a relatively high resistivity, e.g. carbon,provided no limitation is made thereto.

Actually, the surfaces of the conductors 141, 142, 150, 150′, 151 and151′ formed of silver paste for example are also coated with carbon. Oneof the two brushes 13 slides while straddling both resistor R1 andconductor 141, while the other brush 13 slides while straddling bothresistor R2 and conductor 142. The conductors 141, 142 and the brushes13 turn conductive with each other in the thickness direction of thecarbon film at the brush contact positions (the resistance is lowbecause the film thickness is small), so the carbon film formed on theconductors causes no obstacle. Rather, by coating the conductors (silverpaste) with a hard carbon, it is possible to improve the abrasionresistance when the brushes 13 slide on the conductors 141 and 142.

The resistor R1 is formed between ends 151 a and 151 b of a wiringconductor, using only a resistive material. Also as to the resistors R2,R3 and R4, they are formed in the same way.

In FIG. 13, the portions corresponding to the resistors R1, R2, R3 andR4 are hatched. The resistors and wiring layout in FIG. 13 coincide withthe circuit diagram of FIG. 14.

At one end 14 a of the film 14 are disposed a first sensor outputterminal (TPS1) 161, a positive terminal (Vcc) 162 of a power supply, asecond sensor output terminal (TPS2) 163, and a ground terminal (GND)164.

The first sensor output terminal 161 serves as a terminal of the outputtaking-out conductor 141. The conductor 141 is wider at its portionwhere the associated brush 13 slides.

The power supply terminal 162 is connected to one end of the auxiliaryresistor R3 through the conductor 150, while the opposite end of theauxiliary resistor R3 is connected to one end of the resistor R1 throughthe conductor end 151 a and is also connected to one end of the resistorR2 through the conductor end 151 a and the conductor 151. The oppositeend of the resistor R1 is connected to one end of the auxiliary resistorR4 through the conductors 151 b, 151′ and 151 a′. The opposite end ofthe auxiliary resistor R4 is connected to the ground terminal 164through conductors 150 a′ and 150′.

The second sensor output terminal 163 serves as a terminal of the outputtaking-out conductor 142. The conductor 142 is wider at its portionwhere the associated brush 13 slides.

FIG. 14 schematically illustrates a state in which one brush 13 slideswhile straddling the resistor R1 and the conductor 141 and the otherbrush 13 slides while straddling the resistor R2 and the conductor 142.According to the wiring illustrated in FIGS. 13 and 14, if the brushes13 move, for example, in an opening direction from a closed state, thebrush 13 which slides on the resistor R1 moves from a low potential side(ground side) to a high potential side (positive side of the powersupply), while the brush 13 which slides on the resistor R2 moves fromthe high to the low potential side. An equivalent circuit thereof isillustrated in FIG. 15. The sensor output terminals 161 and 162 take outpotentials at the brush contact points of the resistors R1 and R2.

According to the above wiring patterns, the resistors R1 and R2 areconnected at one ends thereof to the positive terminal 162 of the powersupply and at the opposite ends to the ground terminal 164. Further, thecontact positions of the brushes 13 serve as output points for takingout output voltages, the auxiliary resistor R3 is connected between oneends of the resistors R1, R2 and the positive terminal 162 of the powersupply, and the auxiliary resistors R3 and R4 are connected between theopposite ends of the resistors R1, R2 and the ground terminal 164. Inother words, the auxiliary resistors R3 and R4 are provided at both endsof the resistors R1 and R2. The resistors R1 and R2 are each severalkilo-ohms and the resistors R3 and R4 are each several hundred ohms.

FIG. 16 illustrates operational characteristics of sensor outputvoltages relative to movement quantities (throttle valve openings) ofthe brushes 13. In the same figure, the movement quantity 0 correspondsto a fully closed position in control of the throttle valve opening andthe movement quantity 40 corresponds to a fully open position incontrol. The numeral {circle around (1)} represents an operationalcharacteristic at the brush contact point potential in resistor R1 andnumeral {circle around (2)} represents an operational characteristic atthe brush contact point potential in resistor R2. A mean value of bothoperational characteristics {circle around (1)} and {circle around (2)}lies at an intermediate level of potential. If there should occur anytrouble in one of the sensor outputs, the mean value of the operationalcharacteristics {circle around (1)} and {circle around (2)} is biased toeither the upper or the lower side of the above intermediate level. Fromthis bias it is possible to judge which sensor is out of order.

By using the auxiliary resistors 33 and 34 it is possible to make gentlethe gradient of the sensor output characteristics (operationalcharacteristics {circle around (1)} and {circle around (2)}) relative tothe movement quantity of the brushes (throttle valve opening) and hencepossible to diminish output variation characteristics induced by changesin temperature of the resistors for example.

In this connection, reference will now be made, for example, to the casewhere the power supply voltage is 5V and the ground voltage is 0V. Inthis case, in the absence of resistors R3 and R4, a voltage of 5V isapplied to both ends of the resistors R1 and R2, but in the presence ofthe auxiliary resistors R3 and R4 as in this embodiment, the voltage atone ends (the ground side) of the resistors R1 and R2 is raised to ahigher level (say, 0.3V) than zero level because of the presence ofresistor R3, while the voltage at the opposite ends (the positive sideof the power supply) becomes somewhat lower (say, 4.7V) than 5V becauseof the presence of resistor R4. Thus, the potential difference at bothends of the resistors R1 and R2 becomes 4.4V, so that the gradient ofoutput characteristics (operational characteristics {circle around (1)}and {circle around (2)}) relative to the movement quantity of thebrushes becomes smaller than that at the both-end potential differenceof 5V of the resistors R1 and R2 (in the absence of the auxiliaryresistors R3 and R4). Therefore, even where the operationalcharacteristics vary according to temperatures, the variation range ismade narrow to prevent deterioration of the sensor accuracy.

Although in this embodiment the auxiliary resistors R3 and. R4 aredisposed at both ends of the resistors R1 and R2, such an auxiliaryresistor R3 or R4 as described above may be disposed at only one ends ofthe resistors R1 and R2, and even in this case it is possible to narrowthe variation range of the sensor operation characteristics.

As shown in FIG. 13, one end 14 a of the film 14 is made small in widthand the terminals 161˜164 are arranged on one side of the one end 14 a.

On the inner surface of the cover 16, as shown in FIGS. 2 and 7, aterminal box 32 for insertion therein of one end 14 a of the film isformed by the side of the wall portion 15 integrally with the cover 16.

In the terminal box 32, an upper portion 32 a and a side portion 32 bclose to the wall portion 15 are open so that one end 14 a of the filmcan be inserted therein.

At the position of the terminal box 32 the terminals 161˜164 formed atone end of the film 14 and relay terminals 40-1 to 40-4, whichcommunicate with connector terminals, are connected togetherelectrically.

More specifically, as shown in FIG. 9, connector terminals 40 (four inthis embodiment) for external connection of the throttle sensors andconnector terminals 24 (two in this embodiment) for external connectionof the motor power supply are disposed in a connector case 16 b of thecover 16. Conductors 40′ for connection between the connector terminals40 and the throttle sensors and conductors 24′ for connection betweenthe connector terminals 24 and the relay terminals 24 a of the motorpower supply are insert-molded into the cover 16 (this state is shown inFIG. 7 with the conductors partially omitted) and one ends of theconductors 40′, i.e., the terminals 40-1 to 40-4, are erected so as tobe positioned by the side of one end 15 b of the wall portion which isfor holding the curved resistors, in other words, they rise so as toproject upward from the inner surface of the cover 16, further, one ends24 a of the conductors 24′ of the motor power supply are erected fromthe inner surface of the cover 16.

One end 14 a of the film 14 is inserted into the terminal box 32 in sucha manner that the terminals 161˜164 formed on the film 14 and theterminals 40-1˜40-4 conducted into the terminal box 32 confront eachother, and a plate spring 36 serving as a film pressing member isinserted into the terminal box 32, whereby the terminals can beconnected positively without separation. The relay terminals 24 a on themotor side and the motor terminals 23 are connected together through therelay connectors 33.

Advantages of this embodiment are as follows.

-   {circle around (1)} In the throttle sensor, the brushes 13 come into    contact with the curved resistors 14 (R1, R2) while facing in the    radial direction of the throttle valve shaft 3. This is advantageous    in point of reliability.

More particularly, the brushes 13 are mounted on the throttle valveshaft through the holder, but an assembling error developed in thethrottle valve shaft is generally larger in the thrust direction than inthe radial direction. The reason is that variations in machining andvariations in assembly accumulate to 1 mm or so in the radial direction,whereas in the thrust direction there occur only coaxiality deviationand variations among molded products, which can be suppressed to belowseveral hundred micron meters.

Consequently, the separating force of each brush from the associatedresistor induced by wobbling of the throttle valve shaft is larger inthe case where the brush is brought into contact (sliding contact) withthe resistor in the thrust direction of the throttle valve shaft (thecontact in this case is a plane contact) than in the case where thebrush is brought into contact with the resistor in the radial directionof the throttle valve shaft (the contact in this case is a curvedcontact). Therefore, in the former (plane contact) case, it is necessarythat the contact pressure of the brush against the resistor be setlarger than in the latter (curved contact) to prevent the brush and theresistor from coming out of contact with each other. So increasing thecontact pressure will accelerate the wear of the brush and that of theresistor.

This embodiment adopts the latter method, whereby it is possible toprevent the brush-resistor separation without so much increasing thecontact pressure. Consequently, it is possible to enhance thereliability of the throttle sensor and also enhance the abrasionresistance and durability of the sensor components.

-   {circle around (2)} Even in case of adopting such a curved contact    (curved resistor) type throttle sensor (potentiometer) as described    above, this embodiment makes it possible to reduce the number of    components and reduce the product cost. More particularly, for    mounting a curved resistor type sensor into the cover 16 of the    throttle body 1, there may be adopted a different method wherein the    throttle sensor is beforehand unitized separately from the cover and    is then installed into the cover. In this case, however, it is    necessary that sensor components (e.g., resistor, rotor with brush,    and resistor holding member) be accommodated together into a    dedicated unit case (sensor housing). On the other hand, this    embodiment dispenses with such a sensor unit as mentioned above and    permits the gear 12 to serve also as the rotor with brush. In this    embodiment, moreover, since the curved resistor holding member (wall    portion 15) is integral with the cover 16, it is possible to reduce    the number of throttle sensor components and hence reduce the    product cost and simplify the assembling work.

Further, although the curved resistor holding portion is provided in thecover, it is possible to ensure a high sensor accuracy because there isadopted a structure which is difficult to be influenced by thermalexpansion, contraction and deformation of the cover.

-   {circle around (3)} By providing at least one of the auxiliary    resistors R3 and R4 in each throttle sensor it is possible to obtain    operational characteristics of the sensor with suppressed thermal    variation.-   {circle around (4)} It is possible to simplify the bearing structure    of the throttle valve shaft having the throttle sensors; besides, it    is possible to reduce the number of components used and thereby    realize a compact bearing protecting structure.

In more particular terms, according to this embodiment, only one end 3a′ of the throttle valve shaft 3 is projected to the exterior of a sidewall of the throttle body and the reduction gear mechanism and thethrottle sensors are disposed on the throttle body side face on theprojecting side of the throttle valve shaft.

Thus, where the reduction gear mechanism and the throttle sensors arearranged together on one side face of the throttle body, a highlyaccurate bearing such as the ball bearing 6 or any other rolling bearingof reduced wobbling may be used as the bearing for the throttle valveshaft on the side where the above components are arranged, while abearing, e.g., plain bearing, which is less expensive but somewhatinferior in accuracy than the ball bearing, may be used as the otherbearing.

Further, since the plain bearing 26 is cap-shaped and covers one bearingboss 1 b on the throttle valve shaft, it is possible to omit the use ofa dedicated cap or cover for the bearing boss 1 b.

-   {circle around (5)} Additionally, according to this embodiment, at    least one end 15 a of the wall portion 15 which holds the curved    resistor 14 is rounded at 41, so at the time of positioning the    brushes 13 on the curved resistor after installation of the gear 12    and the cover, the brushes 13 can be mounted easily by allowing them    to slide on the rounded surface 41. The numeral 15 c in FIGS. 2 and    3 denotes a stepped portion to be used for positioning the film 14,    the stepped portion 15 c being formed at one end of the wall portion    15. Also for mounting the film 14 to the wall portion 15, for    connecting the sensor terminals and for mounting the brushes, this    embodiment adopts a structure which takes the easiness of those    works into account, thus permitting the reduction of the working    cost.

Although in the above embodiment the film 14 with curved resistors isaffixed to the wall portion 15, the resistors and wiring patterns may beprinted directly onto the surface of the wall portion 15.

INDUSTRIAL APPLICABILITY

According to the present invention, as set forth above, it is possibleto provide a throttle assembly and a throttle sensor, capable ofcontributing to the reduction in the number of components of thethrottle sensor, capable of reducing the manufacturing cost andsimplifying the assembling work and further capable of ensuring highsensor accuracy and reliability.

1. A throttle assembly comprising a throttle body and, as componentsmounted to the throttle body, a throttle valve for controlling the flowrate of intake air in an internal combustion engine, anelectrically-driven actuator for actuating the throttle valve, areduction gear mechanism for the actuator, and a sensor for detectingthe degree of opening of the throttle valve, wherein one end of athrottle valve shaft is projected outwards from a side wall of thethrottle body, said reduction gear mechanism and said sensor aredisposed on a side face of the throttle body on the projecting side ofsaid throttle valve shaft, a bearing which supports one side shaft-partclose to the projecting part of the throttle valve shaft, out ofbearings which support the throttle valve shaft, is a ball bearing, abearing, which supports the other side shaft-part opposite to theprojecting part of the throttle valve is a plain bearing, a cap, and oneend of the plain bearing is covered with a gear of the reduction gearmechanism is fixed on the projecting part of the throttle valve shaft, acoil spring arrangement having a return spring element and a defaultspring element for the throttle valve is provided around a boss for theball bearing and a part of the throttle shaft, and one end of the coilspring arrangement is operatively joined to the throttle body, and theother end thereof is joined to the throttle valve.
 2. The throttleassembly according to claim 1, wherein the plain bearing is cap-shapedwith a cap integrated into the plain bearing, and a bearing mount holeof the boss is closed with the cap-shaped plain bearing.
 3. A throttlesensor for detecting the degree of opening of a throttle valve whichcontrols the flow rate of intake air in an internal combustion engine,wherein the throttle sensor is constituted by a potentiometer whoseoutput varies according to the rotation of the throttle valve, saidpotentiometer comprising a slider adapted to rotate integrally with athrottle valve shaft and a resistor on which the slider slides, theresistor being connected at one end thereof to a positive-side terminalof a power supply and at the other end thereof to a ground-side terminalwherein the resistor is comprised of a first resistor element and asecond resistor element which are divided so as to be parallel with eachother and connected in parallel between the positive side terminal ofthe power supply and the ground side terminal, the first and the secondresistor elements are connected to the positive side terminal through afirst auxiliary resistor and connected to the ground side terminalthrough a second auxiliary resistor, additionally a first conductor anda second conductor are placed alternately together with the first andthe second resistor elements in parallel, each one end of the conductorsis opened, the other end thereof is each an output terminal, and theslider is comprised of two slider elements which are slidable togetherin the same direction, and one of the slider elements is slidablebetween the first resistor element and the first conductor, and theother of the slider elements is slidable between the second resistorelement and the second conductor.
 4. The throttle sensor according toclaim 3, wherein the slider is fixed on a resin gear.
 5. The throttlesensor according to claim 4, wherein the resin gear has a metallic platehaving a shaft through-hole, and being fixed on the resin gear by insertmolding, and the resin gear is fixed on the projecting part of thethrottle shaft through the metallic plate.
 6. The throttle sensoraccording to claim 4, wherein a resin portion of the gear has integratedresin lugs, the slider has through-holes for the lugs, and the slider isfixed at the gear by crushing with heat the lugs inserted thethrough-hole.
 7. The throttle sensor according to claim 3, wherein thefirst and the second resistor elements have values of several kilo-ohms,and the auxiliary resistor have values of several hundred-ohms.